In general, a lower traveling structure of a crawler-type vehicle such as a hydraulic excavator is substantially composed of a truck frame having left and right side frames, a drive unit provided on one end side of each of the side frames, an idler wheel (idler) provided on the other end side, a crawler belt set on a drive wheel (sprocket) and the idler wheel of the drive unit, and upper and lower crawler belt guide rollers which guide the crawler belt toward the drive wheel and the idler wheel, respectively. The above-described drive unit, idler wheel, crawler belt guide rollers and the like constitute a rotation device for a construction machine.
The crawler belt guide roller is substantially composed of a shaft support member (fixed body) provided on the side frame in a fixed manner and having a bottomed seal accommodating portion formed, a support shaft fixed to this shaft support member, a roller (rotating body) rotatably supported by the support shaft through a bush (slide bearing) and having a bottomed seal accommodating portion formed opposing the seal accommodating portion of the shaft support member with a gap between them and lubricant oil collected inside, and a floating seal arranged in the seal accommodating portion of the shaft support member and the seal accommodating portion of the roller and blocking the gap between the both.
In this case, the floating seal is composed of a pair of cylindrical seal rings, each having a sealing surface in sliding contact with each other, and a pair of O-rings held between one of the seal rings and the seal accommodating portion of the shaft support member and between the other seal ring and the seal accommodating portion of the roller, respectively. The floating seal presses each of the seal rings by an elastic force of the O-rings all the time so as to bring the sealing surfaces into sliding contact with each other in a liquid-tight manner when the roller is rotated with respect to the shaft support member and seals the lubricant oil supplied to the bearing which supports the roller and the like inside the roller (Japanese Patent Laid-Open No. 2001-80550 A).